This invention relates to the field of automatic inspection and, more particularly, to an apparatus for inspecting the surface of an object using a beam of radiation, such as a laser beam.
The automatic inspection of parts with a laser beam is gaining widespread commercial acceptance. For example, in my U.S. Pat. Nos. 3,816,746 and 3,983,388, assigned to the same assignee as the present application, there are disclosed apparatus for automatically inspecting hardware items by scanning a laser beam over a threaded surface of a hardware item at an inspection position and then detecting the nature of the reflected energy to determine the presence of defects or count threads, etc. Various other systems are also available for scanning surfaces with a laser beam and determining the properties of the surface by detecting the characteristics of the laser light reflected from the surfaces. In general, the scan of the inspecting beam is linear in nature, usually being either a line scan or a field scan made up of line scans. These types of scans are suitable for inspecting many types of surfaces and, for some applications, they can be generated and tracked for detection without undue system complexity.
Many objects, for example gears, bearing races, and tampon ends, are not conveniently inspected using a linear scan since they have generally circular surface or circular symmetry which would be more efficiently inspected using a substantially circular scan. Techniques for obtaining a circular scan of a light beam are known in the art. However, there are problems associated with generating such a beam for inspection purposes, and then collecting the radiation reflected off the inspected object's surface. For example, it is necessary that the collecting optics not interfere with the scanning beam, while maintaining the collection efficiency as high as possible. Also, the optical system should ideally be kept as simple as possible to minimize cost. Further, the need for expensive detector arrays, which introduce unreliability and expense, should be avoided, if possible.
It is one object of the present invention to provide an apparatus for inspecting the surface of objects with a substantially circular scan, the apparatus operating at relatively high efficiency with a minimum of parts and requiring only a simple detector.